(a) Field of the Invention
The present invention relates to a dummy pad, a printed circuit board including the same, and a liquid crystal display including the same.
(b) Description of the Related Art
Generally, a liquid crystal display includes a display panel, a TAB-IC (tape automated bonding integrated circuit) and a PCB (printed circuit board). They are electrically connected to each other through pads formed therein, and the TAB-IC has a soldering pad portion and an OLB (out lead bonding) pad portion. Here, the TAB-IC and the PCB are connected to each other by soldering pads of the soldering pad portion of the TAB-IC and of the pad portion of the PCB.
A soldering pad portion of the TAB-IC and a pad portion of the PCB have signal pads delivering scanning signals or image signals, and dummy pads, which are located near the edges of the soldering pad portion of the TAB-IC a and the pad portion of the PCB, delivering reference voltage, ground voltage or common voltage. The sizes of most signal pads are similar, but the sizes of the dummy pads are twice or triple as large as the size of the signal pads.
In the meantime, the pads of the TAB-IC and of the PCB are soldered by the flowing steps. Solder layers are printed on the pads of the pad portion of the PCB. The solder layers are melted by reflow process to form solder drops. Finally, the solder drops are melted again and the pads are adhered by applying pressure. It is desirable that the heights of the solder drops on the pads are equal. It is because unequal heights of the solder drops on the pads generate the microcrack or microgaps between the pads and the solder layers. However, because the areas of the dummy pads are larger than those of the signal pads and the sizes of the openings of the printing mask are substantially equal to the sizes of the pads, it is difficult to adjust the amount of the solder on the dummy pads such that the heights of the melted solder drops are equal. In addition, if the amount of the printed solder on the dummy pads is excessive, the adjacent pads may be short-circuited, while if insufficient amount of the solder causes the reliability of the soldering to be reduced.